Jamieson, Fausset and Brown on James 1:4

4. Let endurance have a perfect work (taken out of the previous "worketh patience" or endurance), that is, have its full effect, by showing the most perfect degree of endurance, namely, "joy in bearing the cross" [Menochius], and enduring to the end (Mt 10:22) [Calvin].

ye may be perfect--fully developed in all the attributes of a Christian character. For this there is required "joy" [Bengel], as part of the "perfect work" of probation. The work of God in a man is the man. If God's teachings by patience have had a perfect work in you, you are perfect [Alford].

entire--that which has all its parts complete, wanting no integral part; 1Th 5:23, "your whole (literally, 'entire') spirit, soul, and body"; as "perfect" implies without a blemish in its parts.